Body level concepts

Gross and Microscopic Anatomy

¹

1. Gross anatomy considers large structures such as the brain.

2. Microscopic anatomy can deal with the same structures, though at a different scale. This is a micrograph of nerve cells from the brain. LM × 1600.

(slide credit: @OpenStaxAnatomy2020)

Levels of Structural Organization of the Human Body

(Modified from: @OpenStaxAnatomy2020)

Organ Systems of the Human Body

Organs that work together are grouped into organ systems.

(Modified from: @OpenStaxAnatomy2020)

Anatomical Terms

Directional Terms Applied to the Human Body

Paired directional terms are shown as applied to the human body.

(slide credit: @OpenStaxAnatomy2020)

Planes of the Body

The three planes most commonly used in anatomical and medical imaging are the sagittal, frontal (or coronal), and transverse plane.

(slide credit: @OpenStaxAnatomy2020)

Relative reference terms

• Proximal/Distal aspect
  • Nearer to/Further from the origin or attachment point
• Inferior/Superior
  • Beneath/Above: Often used in the axial skeleton
• Cranial/Caudal
  • Towards/Away from the head
• Lateral/Medial
  • Closest to the outside/inside relative to the mid-line in the coronal plane
• Anterior/Posterior
  • In front/back (relative position)
• Dorsal/Ventral
  • On the back/front

Terms of action

• Flexion/Extension
  • The anterior angle between two bones is decreased/increased (except for knees/toes, then posterior angle)
• Abduction/Adduction
  • Movement away from/towards the body mid-line in the frontal plane
• Lateral flexion
  • Left/right movement of the spine in the frontal plane
• Supination/Pronation
  • Rotate the forearm palm forward/backward in the anatomical position
• Dorsiflexion/Plantar flexion
  • Rotation of the ankle toes up/down in the sagittal plane
• Inversion/Eversion
  • Rotation of the foot up and in/up and out in the frontal plane
• Hyperextension
  • Movement beyond anatomical norms

Principal functions of the musculoskeletal system

Critical functions of the bones

• Hematopoiesis (formation of red blood cells)
• Mineral storage (99% of body’s calcium)
  • Insufficient calcium intake thus leads to:
    • a reduction of calcium storage in the bones and a corresponding reduction the bones’ “mechanical properties”
    • an increased fracture risk
• Protection of the vital organs
• Support and motion

Hematopoiesis

Elements of the Human Body

The main elements that compose the human body are shown from most abundant to least abundant.

(slide credit: @OpenStaxAnatomy2020)

Protection of the vital organs

• Distribute loads (stiff cortical bone)
• Absorb energy (softer cancellous bone)

Examples follow:

Bones protect the brain

• The cranium completely surrounds and protects the brain from traumatic injury
  • Distributes load and absorbs energy
• Others protective bones
  • Ribs, spinal cord, etc

Support and motion

• Provide a framework for force and motion necessary for living
• Bone and joints act as levers, muscles act as actuators
• Muscles apply forces at some moment arm, creating torques to rotate a joint

• Consequences of muscle attachment points (relative to joint position)?
  • Disadvantage – loads on joints and muscles are larger than the functional loads applied to the body
  • Advantage – small muscle displacements cause large rotations and fast motion

Principal anatomical structures examined to this course

• Bones of the skeleton
• Joints
• Soft tissue

Bones

Major boney structures examined in this course

The human body is shown in anatomical position in an (a) anterior view and a (b) posterior view. The regions of the body are labeled in boldface.

• There are typically 206 bones in the human body (+4 sesamoid bones in the foot)
• Can be categorized into roughly 4 groups
  • Long bones (femur, tibia, humerus, etc)
    • Long in one direction, tubular cross sections
  • Short bones (wrist, ankle, hand, foot, etc)
    • Have similar dimensions in all directions
  • Flat bones (scapula, skull, pelvis, etc)
    • Are short in one dimension relative to the others
  • Irregular
    • Those that don’t easily fit into the other categories

Bone tissue types

Long bone

• Implants often interface with the medullary cavity as a means of attachment (ie intramedullary nail)
• The epiphysis (bone end) grows from separate ossification centers at the end of the bone
• Metaphysis is the region between the diaphysis and the epiphysis

Anatomy of a Long Bone

A typical long bone shows the gross anatomical characteristics of bone.

(slide credit: @OpenStaxAnatomy2020 Ch. 6)

Periosteum and Endosteum

The periosteum forms the outer surface of bone, and the endosteum lines the medullary cavity.

(slide credit: @OpenStaxAnatomy2020 Ch. 6)

Anatomy of a Flat Bone

This cross-section of a flat bone shows the spongy bone (diploë) lined on either side by a layer of compact bone.

(slide credit: @OpenStaxAnatomy2020 Ch. 6)

Bone Features

The surface features of bones depend on their function, location, attachment of ligaments and tendons, or the penetration of blood vessels and nerves.

(slide credit: @OpenStaxAnatomy2020 Ch. 6)

Joints

Joints can be classified functionally or structurally

• Functional classification depends on the amount of relative motion… less convenient
  • Large motions – diarthrodial joint
• Structural classification depends on joint mechanism

Structural classification of joints

• Fibrous (or Immovable) joints
  • Held together by a thin layer of strong connective tissue
  • No movement between the bones such
    • Sutures of the skull
    • Teeth in their sockets
• Cartilaginous joints
  • Bones attached by white fibrocartilaginous discs and ligaments
  • Limited degree of movement
    • Intervertebral discs
    • The cartilage in the symphysis (binds the pubic bones together at the front of the pelvic girdle)
    • The cartilage between the sacrum and the hip bone

• Synovial joints (subset of diarthrodial joints)
  • Covered with a layer of smooth articular (hyaline) cartilage
  • Enclosed by a bag-like capsular ligament which constrains the joint and helps contain the synovial fluid
  • The capsular ligament is lined with a synovial membrane. This membrane secretes synovial fluid into the cavity as a lubricant
  • In addition to the capsule, the bones are constrained by other strong ligaments
  • Very low friction coefficient
    • human knee – \(\mu=0.005-0.02\)
    • human hip – \(\mu=0.01-0.04\)
    • Lower than most engineered structures

Synovial joints

• Ball and socket
• Condylar joints
• Multiple bone joints (Compound Joints)

Ball and socket

AP Hip, AP Shoulder, and Axial Shoulder X-rays ²

• The rounded head interfaces the cup-shaped socket of another
  • Hip
    • Femoral head (ball) and acetabulum (socket)
  • Shoulder
    • Humeral head (ball) and glenoid (socket)
    • The glenoid is nearly flat… thus the shoulder requires significant soft tissue for stabilization

Bi-condylar joints

³

• The condyles are the enlarged regions at knuckles of any joint.
  • They are enlarged, in part, to minimize the stresses of load transfer.
  • Examples: medial and lateral condyles of the femur and tibia

Bi-condylar joints

• “Bi” - Pairs of articulating surfaces
• Two curved condyles articulate against relatively flat surfaces of the mating bone
• There is little kinematic constraint, thus, extensive soft tissue is required for stability.

• Having two condyles allows for resistance to moments in planes perpendicular to the plane of motion.
  • The two condyles and their supporting soft tissues only allow small angular rotations in planes perpendicular to the intended plane
    • Less muscular restraint required about these planes

• These joints have extensive range of motion in one plane
  • ie the knee has extensive flexion/extension in the sagittal plane

Multiple bone joints

AP Hip, Oblique, and Lateral X-rays of the Foot ⁴

Multiple bone joints

• More difficult to describe than ball-and-socket or bi-condylar joints
• Examples: wrist (8 carpal bones), ankle (7 tarsal bones)
• Bound by lots of ligaments and have synovial fluid
• Small motions between individual joints add up to larger motions